This pilot study of 20 patients is designed to evaluate: 1) the CD34+ cell mobilization response to administration of standard doses of granulocyte-colony stimulating factor (G-CSF) and 2) the potential for collecting stem cells from patients with a history of severe AA who have been given G-CSF. Outcome parameters to be monitored are the mobilization response to G-CSF, and the safety profile and tolerance of G-CSF and leukapheresis. Effectiveness will be gauged by historical comparison of these parameters to normal healthy age-matched volunteers.